Cooler control system for automobile coolers

ABSTRACT

A cooler control system suitable for automobile coolers. It includes an engine speed detection circuit and a temperature control circuit to control the operation of a cooler through the combination of these circuits, thereby separating the cooler from the engine to reduce the engine load during low engine speed operation so as to overcome the insufficiency of the engine output under the low engine speed operating condition. The engine speed detection circuit of the cooler control system according to the invention includes an integrating capacitor, whose discharging circuit comprises a transistor, diode and resistor, whereby the fluctuation of the preset engine speed is prevented.

Unite States Patent Yonezu [54] COOLER CONTROL SYSTEM FOR AUTOMOBILE (IOOLERS [72] Inventor: Hisashi Yonezu, Aichi, Japan [73] Assignee: Nippondenso Kabushiki Kaisha, Showacho, Kariya-shi, Aichi-ken, Japan 22 Filed: Dec. 28, 1970 21 Appl.No.: 101,775

[30] Foreign Application Priority Data Jan. 13, 1970 Japan ..45/4294 [52] US. Cl. ..62/l33, 62/230 [51] Int. Cl ..B60h 3/04 [58] Field of Search ..62/133, 323, 230; 123/32 EA;

[56] References Cited UNITED STATES PATENTS Pruitt ..62/323 X 3,463,130 8/1969 Reichardt et al. ..123/32 EA Primary Examiner-William E. Wayner AttorneyCushman, Darby & Cushman ABSTRACT A cooler control system suitable for automobile coolers. It includes an engine speed detection circuit and a temperature control circuit to control the operation of a cooler through the combination of these circuits, thereby separating the cooler from the engine to reduce the engine load during low engine speed operation so as to overcome the insufficiency of the engine output under the low engine speed operating condition. The engine speed detection circuit of the cooler control system according to the invention includes an integrating capacitor, whose discharging circuit comprises a transistor,

' diode and resistor, whereby the fluctuation of the preset engine speed is prevented.

2 Clairm, 7 Drawing Figures COOLER CONTROL SYSTEM FOR AUTOMOBILE COOLERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to cooler control system for automobile coolers and, more particularly, to a cooler control system including an engine speed detection circuit and a temperature control circuit.

2. Description of the Prior Art The conventional cooler control system for controlling automobile coolers includes an engine speed detection circuit having an integrating capacitor, which is charged and discharged in accordance with the engine speed. When the engine speed is reduced to a preset speed, the terminal voltage across the integrating capacitor is increased to reach a predetermined value to thereby detect the preset engine speed. The discharging circuit of the integrating capacitor of the engine speed detection circuit, however, usually comprises only a transistor and a diode, and hence, as the internal resistances of the transistor and diode widely vary due to their tolerances in production, the preset engine speed tends to vary with different engine speed detection circuits of the same design and construction.

Also, in the conventional cooler control system an electromagnetic clutch for engaging and disengaging the cooler with the engine is controlled independently by an engine speed detection circuit and by a temperature detection circuit, so that the output circuits of these two circuits tend to overlap each other. This is clearly disadvantageous in respect of economy.

SUMMARY OF THE INVENTION An object of the present invention is to provide a cooler control system, wherein an integrating circuit of the engine speed detection circuit comprises a capacitor; a first resistor in a charging circuit thereof; and a transistor, a diode and a second resistor in a discharging circuit thereof, thereby minimizing the deviation of an engine speed from a preset value so as to prevent the overheating of the engine.

Another object of the invention is to provide a cooler control system, which includes an engine speed detection circuit and a temperature control circuit to achieve control of the cooler through the combination of these circuits, whereby the cooler is separated from the engine to reduce the engine load during low engine speed operation or when the temperature of a passenger room is low, so as to provide for an insufficient engine output of a small-sized automobile engine under low engine speed operating conditions, and to simplify the circuit of the cooler control system.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a circuit diagram showing an embodiment of the cooler control system according to the invention.

FIGS. 2a to 2d are graphs showing waveforms of voltages appearing on various parts of the engine speed detection circuit in the system according to the invention.

FIG. 3 is a graph showing the resistance-temperature characteristic of a heat-sensitive element of the temperature control circuit in the system according to the invention.

FIG. 4 is a graph showing the relationship between angle of the rotary slide of a temperature regulation variable resistor and the ambient temperature about a heat-sensitive element characterizing the system according to the invention.

In FIG. 1, reference numeral 1 designates a DC. source, numeral 2 an ignition coil, and numeral 3 breaker contacts. Numeral 4 designates a control system according to the invention, which has an engine speed detection input terminal 4a, an earth terminal 4b, a source terminal 40, an output terminal 4d, a temperature detection input terminal 4e, and a feedback terminal 4f. Numeral 5 designates an electromagnetic clutch to switch between a cooler (not shown) and an engine. It is connected between the output terminal 4d and ground. Nu-

meral 6 designates a temperature regulation variable resistor connected to the terminal 4e, and numeral 7 a thermistor connected between the variable resistor 6 and ground. The connection between the variable resistor 6 and the thermistor 7 is connected to the feedback terminal 4f. The input terminal 4a is connected through resistors 8 and 9 to the base of a transistor 12. A resistor 11 is connected between the base of the transistor 11 and the earth terminal 4b. The connection between the resistors 8 and 9 is connected through a capacitor 10 to the earth terminal 4b. The emitter of the transistor 12 is connected through a resistor 14 to the earth terminal 4b. The collector of the transistor 12 is connected both to a resistor 13 and a capacitor 15. The other end of the capacitor 15 is connected to the base of a transistor 17, and the other end of the resistor 13 is connected to the source terminal 4c. A resistor 16 is connected between the base of the transistor 17 and the earth terminal 4b. The emitter of the transistor 17 is connected through a diode 19 to the earth terminal 4b. The collector of the transistor 17 is connected through a resistor 40 to a resistor 18, a capacitor 20 and a resistor 21. The other end of the resistor 18 is connected to a source terminal 40, the other end of the capacitor 20 is connected directly to the earth terminal 4b, and the other terminal of the resistor 21 is connected through a variable resistor 22 and a resistor 23 to the earth terminal 4b. The variable resistor 22 has its slide terminal connected to the base of a transistor 24. The emitter of the transistor 24 is connected to the emitter of a transistor 31 and through resistors 32 and 33 to the earth terminal 4b. The collector of the transistor 24 is connected to a resistor 38, the base of the transistor 31 and to the collector of the transistor 30. The other terminal of the resistor 38 is connected to the source terminal 4c. The base of the transistor 30 is connected through a resistor 27, a variable resistor 28 and a resistor 25 to the source terminal 4c. A zener diode 26 is connected between the earth terminal 4b and the connection between the resistor 25 and variable resistor 28. The connection between the resistors 27 and 29 is connected to the temperature detection input terminal 4e. The emitter of the transistor 30 is connected to the connection between the resistors 32 and 33. The collector of the transistor 31 is connected to a coil 34a of the relay 34, a diode 36 and a resistor 35. The diode 36 and the relay coil 340 have their other ends connected to the source terminal 4c. The resistor 35 has its other end connected through a feedback resistor 39 to the feedback terminal 4f. The connection between the resistors 35 and 39 is connected through a capacitor 37 to the earth terminal 4b. The relay 34 has its contacts 34b inserted between the source terminal 4c and the output terminal 4d.

The operation of the construction described above will now be described. First, the operation of the engine speed detection circuit is given in detail. The breaker contacts 3 are on-off operated in accordance with the engine speed, so that a pulse train appears across the terminals 4a and 4b. The number of pulses per unit time and pulse width of the pulses in the pulse train vary in accordance with the engine speed, as shown in FIG. 2a. In FIGS. 2a to 2d, the ordinate represents voltage V and the abscissa represents time t. The resistors 8, 9, l1, l3 and 14, the capacitor 10 and the transistor 12 form a shaper circuit, which produces a square pulse train appearing between the collector of the transistor 12 and the earth terminal 4b, as shown in FIG. 2b. The capacitor 15 and resistor 16 constitute a differential circuit whose output voltage, i.e., the terminal voltage across the resistor 16 has a waveform as shown in FIG. 20. The transistor 17, resistors 40 and 18 and diode 19 form a shaper circuit providing a square pulse train appearing between the connection point B between the resistors 40 and 18 and the earth terminal 4b, as shown in FIG. 2d. The waveform shown in FIG. 2d will appear directly on the base of the transistor 24 if the circuit of the capacitor 20 and resistor 21 were absent. The pulse width T for this pulse train is constant irrespective of the number of pulses per unit time. Thus, a pulse train, whose number of pulses per unit time varies with the engine speed, and for which the pulse width is constant, may be obtained. In other words, the number of pulses having a constant pulse width per unit time is increased with increase in the engine speed. By connecting the integrating capacitor between the connection point B and the earth terminal 4b, the terminal voltage across the capacitor 20 becomes as shown by a dashed line in FIG. 2d. As the number of pulses of constant pulse width T increases with increase of engine speed the terminal voltage across the integrating capacitor 20 is gradually decreased. On the other hand, as the number of pulses decreases with decrease of the engine speed the terminal voltage across the integrating capacitor 20 is gradually increased. The charging time for the capacitor 20 depends upon the resistance of the resistor 18, while the discharging time depends upon the resistance of the resistor 40. With decrease in the terminal voltage across the capacitor 20 the base potential of the transistor 24 is decreased, cutting off the collector-emitter path of the transistor 24 to cause current to flow from the DC. source 1 through the resistor 38 into the base of the transistor 31, thus triggering the transistor 31, so that the switch contacts 34b of the relay 34 are closed to render the electromagnetic clutch 5 operative. Thus, the electromagnetic clutch 5 is not operative when the engine speed is low, and it becomes operative to start the cooler when the engine speed reaches a certain predetermined value determined by the variable resistor 22. In this manner, the cooler is automatically separated from the engine to relieve the engine of its load during the low speed engine operation, so that smooth driving of a vehicle provided with a small-size engine tending to provide insufficient engine output under low engine speed operating condition may be ensured even during low engine speed operation.

Next, the operation of the temperature control circuit is given in detail. The thermistor 7 is provided in the vicinity of the evaporator of the cooler, and its resistance remains low when the ambient temperature is high. Assuming that the temperature regulation variable resistor 6 is set to 00, when the resistance of the thermistor 7 is low, the base potential of the transistor 30 is low, so that the transistor 30 is off. Under this condition, upon cutting-off of the transistor 24 to cause current to flow from the DC. source 1 through the resistor 38 into the base of the transistor 31, the transistor is triggered, causing current to pass through the coil 34a of the relay 34. When the coil 34a is energized, the contacts 34b of the relay 34 are closed to render the electromagnetic clutch 5 operative, thus starting the cooler. With the start of the cooler, the ambient temperature about the thermistor 7 begins to gradually fall. The collector potential of the transistor 31 at this time is substantially equal to the ground potential (because the resistance of the resistors 32 and 33 is set sufficiently low as compared to the DC. resistance of the coil 34a). Thus, at this time the feedback resistor 39 can be regarded to be grounded through the resistor 35 and is in parallel with the thermistor 7. When the ambient temperature about the thermistor 7 is reduced to t in FIG. 3 (in which the ordinate represents resistance R of the thermistor 7 and the abscissa represents the ambient temperature t about the thermistor 7), the resistance of the thermistor 7 reaches R Thereupon, the transistor 30 will be triggered to cut ofi the transistor 31 by setting such that:

I/ 21 25 4) 2 ar: where R is the resistance of the resistor 27, R is the resistance of the resistor 28, V is the zener voltage of the zener diode 26, V is a base voltage with which the collectoremitter path of the transistor 30 is triggered, and R is given as:

R4 (R4 X ae/ 4 R39) R4 R39,

with R being the resistance of the feedback resistor 39. Since the resistor is sufiiciently small as compared to the resistance of the feedback resistor 39, it is omitted in the above equation. Upon cutting-off of the transistor 31 the coil 34a of the relay 34 is deenergied to open the contacts 34b of the relay 34, thus rendering the clutch 5 inoperative to stop the cooler, whereupon the ambient temperature about the thermistor 7 begins to gradually rise. Also, upon the cutting-off of the transistor 31 the collector potential of the transistor 31 is increased substantially to the source potential, so that current is caused to flow from the DC. source 1 through the path of the feedback resistor 39 into the base of the transistor 30, into which current also flows from point A through the resistors 28 and 27. Thus, the transistor 30 will not be cut off even when the resistance of the thermistor 7 gets lower than R with subsequent increase of the ambient temperature, but it is cut off only when the resistance of the thermistor 7 is reduced to R for which the ambient temperature about the thermistor 4 is 1 The temperature difference At given as A! r r represents a hysteresis temperature width.

in the above manner, the lowest temperature is determined, when the temperature regulation variable resistor 6 is set to 09. By increasing the resistance of the temperature regulation variable resistor 6, the transistor 30 will be triggered to render the electromagnetic clutch 5 inoperative before the resistance of the thermistor 7 reaches R so that the ambient temperature about the thermistor 7 begins to rise gradually before R is reached. Since the lowest temperature of the room results when the temperature regulation variable resistor 6 is set to 09, it can be correctly determined without being affected by the fluctuation of the resistance of the variable resistor 6. The temperature of the room in the high temperature range is subject to deviation due to the fluctuation of the resistance of the temperature regulation variable resistor 6. This deviation, however, will not result in the frosting of the evaporator, so it presents no practical problem. The hysteresis temperature width has heretofore been obtained by a method employing a well-known Schmitt circuit having an emitter common resistor and a method using a circuit, which is similar to that according to the invention, but in which the feedback resistor 39 is connected to the terminal 4f. The latter method has the same effects as described above so long as the temperature regulation variable resistor 6 is set to 0Q in this method, a division of the base potential V just sufficient to trigger the transistor 30 appears across the resultant series resistance offered by temperature regulation variable resistor 6 and thermistor 7. Thus, when the resistance of the temperature regulation variable resistor 6 is 00, i.e., minimum, the resistance of the thermistor 7 is maximum, which is R while when the resistance of the temperature regulation variable resistor 6 is maximum, the base voltage V is reached when the resistance of the thermistor 7 takes a lower value of R for which the ambient temperature about the thermistor is t In this manner, temperature control over a range between t, and t may be achieved by the temperature regulation variable resistor 6. However, connecting the feedback resistor 39 to the terminal 4f as described above has a disadvantage that the hysteresis temperature width is extremely large in case the temperature regulation variable resistor 6 is set to the maximum value R The thermistor 7 has a characteristic that the change in resistance per temperature change of 1 C. is high in the high resistance region and low in the low resistance region. Since R4 R2 mari the current flowing through the feedback resistor 39 into the base of the transistor 30 when the resistances of temperature regulation variable resistor 6 and thermistor 7 are respectively 00 and R is the same as when their resistances are respectively R and R Thus, for the hysteresis resistance width:

Therefore, for the low resistance region the transistor 30 is cut ofi only when the resistance of the thermistor 7 is reduced to R corresponding to an ambient temperature of t As is apparent from FIG. 3,

t 1 r which is unfavorable is practice. Experiments indicate that if At is equal to 3 C. with t, equal to 3 C. and t equal to 0 C., by setting to be equal to 15 C. with t is equal to 24 C. requiring a hysteresis temperature width At of 9 C. Thus, the

hysteresis temperature width for the high temperature range as in the case when setting the temperature regulation variable resistor 6 to the maximum value is very large, experimentally three times as large, as compared to the hysteresis temperature width for the low temperature range as when the temperature regulation variable resistor 6 is set to 00. The aforementioned method of using a Schmitt circuit has the same disadvantage that the hysteresis temperature width is very large for the feedback amount is determined by the emitter common resistor.

The control system according to the invention is constructed to overcome the above disadvantage. According to the invention, as the feedback resistor 39 is connected to the connection between temperature regulation variable resistor 6 and thermistor 7, the base current passing through the feedback resistor 39 into the transistor 30 also passes through the temperature regulation variable resistor 6, so that the amount of feedback via the feedback resistor 39 is reduced. This aids the cutting-off of the transistor 30 at an early instant in case the transistor 30 is to be cut off at a low value of the resistance if the thermistor 7, that is, in case of a high resistance of the temperature regulation variable resistor 6. The current fed back through the feedback resistor 39 is maximum when the temperature regulation variable resistor 6 is set to 00, while it is minimum when the resistance of the feedback resistor 6 is set to the maximum. Thus, it may be said that in this circuit the characteristics of the thermistor 7 is taken into due consideration.

In consequence, if the resistance of the temperature regulation variable resistor 6 is maximum, the electromagnetic clutch 5 is rendered inoperative when the ambient temperature is reduced to 1 and rendered operative when the ambient temperature is increased to 1,. Thus, the hysteresis temperature difference (t t in the high temperature region may be made equal to the hysteresis temperature difference (t L in the low temperature region.

FIG. 4 shows the relationship between angle 6 of the rotary slide of the temperature regulation variable resistor 6 and ambient temperature T. In the figure, plot A represents the instant at which the electromagnetic clutch 5 is rendered operative, and plot B represents the instant at which the electromagnetic clutch 5 is rendered inoperative. The maximum angle of the rotary slide is indicated at M. The relevant potential at point A is determined by the zener voltage of the zener diode 26 and is free from fluctuation. Thus, in the system according to the invention the preset temperature is substantially free from fluctuations due to fluctuations of the source voltage. Also, the effects of the noise pulses from the ignition system upon the temperature control circuit is prevented by a filter circuit consisting of the resistor 35 and the capacitor 37.

In the circuit construction described above, the resistors 32 and 33 serve to impart a hysteresis character to the switching action of the transistor circuit consisting of the transistors 24 and 31. The hysteresis characteristic of the switching action of the transistor circuit including the transistors 30 and 31 may be adjusted by means of one of the resistors 32 and 33, namely resistor 33, to adjust the hysteresis temperature difference between plots A and B in FIG. 4. Thus, it is possible to adjust the hysteresis temperature difference between the plots A and B not only through the feedback resistor 39 but also the resistor 33. Similar to the well-known Schmitt circuit, the resistor 33 aids in effect to cause the switching action of the transistor circuit earlier for slow change in the resistance of the thermistor 7.

As has been described in the foregoing, according to the invention the transistor of the differentiating and shaping circuit in the engine speed detection circuit has its collector connected through a series circuit of two resistors to the power supply and the capacitor of the integrating circuit is connected to the connection between said two resistors, one of which determines the charging time for said capacitor, and the other of which determines the discharging time for said capacitor, so

that it is ossible to preset the charging time and discharging time of t e capacitor of the integrating circuit independently of each other. For instance, if the discharging time is set to be long by using a large resistance for the resistor 40, the charging time may also be extended by increasing the resistance of the resistor 18. Increasing the resistance of the resistor 18 has an effect of reducing the charging voltage with which to charge the capacitor 20 (the voltage built up when the capacitor 20 is fully charged) to enable reducing the breakdown voltage of the capacitor 20. Also, since the extent of discharging from the capacitor 20 depends upon the resistor 40, the discharging extent may be reduced by increasing the resistance of the resistor 40 so as to reduce the capacitance of the capacitor 20. Without the resistor 40, the discharging time for the capacitor 20 depends upon the saturation voltage across the collector-emitter of the transistor 17 and upon the forward rise-up voltage of the diode 19. These voltages are subject to considerable fluctuations introduced in the manufacture of the transistor and diode, causing fluctuations of the present values of the engine speed. By the provision of the resistor 40 according to the invention, the effects of the fluctuations of the ratings of the transistor and diode upon the discharging time for the capacitor 20 become too slight to present any practical problem to the great advantage that a correct present value of the engine speed may be achieved.

I claim:

1. A cooler control system for controlling automobile coolers comprising:

an engine speed detection circuit including a shaping circuit for shaping a pulse train produced in accordance with the engine speed, a differentiating and shaping circuit for differentiating the output pulses of said shaper circuit and shaping the resultant pulses into square pulses of a constant pulse width, and an integrating circuit for integrat ing the constant-width pulses so as to produce a DC. voltage corresponding to the engine speed, said differentiating and shaping circuit having a transistor with the collector connected to a power source through a series circuit constituted by two resistors, said resistors of said series circuit respectively determining a charging time and a discharging time for a capacitor of said integrating circuit, and said capacitor being connected to a junction point of said resistors of said series circuit;

a temperature control circuit; and

a transistor circuit for starting a cooler only when at least one of the output signals of said engine speed detection circuit and said temperature control circuit reaches a corresponding one of preset values thereof.

2. A cooler control system as defined in claim 1, wherein said temperature control circuit includes a second series circuit having a temperature regulation variable resistor and a temperature detection heat-sensitive element connected in series, said temperature control circuit providing an output voltage signal appearing across said second series circuit, and said transistor circuit for controlling a cooler has an output terminal connected through a feedback resistor to a junction point of said variable resistor and said heat-sensitive element, the feedback current through said feadback resistor being varied according to a change in a resistance value of said variable resistor. 

1. A cooler control system for controlling automobile coolers comprising: an engine speed detection circuit including a shaping circuit for shaping a pulse train produced in accordance with the engine speed, a differentiating and shaping circuit for differentiating the output pulses of said shaper circuit and shaping the resultant pulses into square pulses of a constant pulse width, and an integrating circuit for integrating the constant-width pulses so as to produce a D.C. voltage corresponding to the engine speed, said differentiating and shaping circuit having a transistor with the collector connected to a power source through a series circuit constituted by two resistors, said resistors of said series circuit respectively determining a charging time and a discharging time for a capacitor of said integrating circuit, and said capacitor being connected to a junction point of said resistors of said series circuit; a temperature control circuit; and a transistor circuit for starting a cooler only when at least one of the output signals of said engine speed detection circuit and said temperature control circuit reaches a corresponding one of preset values thereof.
 2. A cooler control system as defined in claim 1, wherein said temperature control circuit includes a second series circuit having a temperature regulation variable resistor and a temperature detection heat-sensitive element connected in series, said temperature control circuit providing an output voltage signal appearing across said second series circuit, and said transistor circuit for controlling a cooler has an output terminal connected through a feedback resistor to a junction point of said variable resistor and said heat-sensitive element, the feedback current through said feadback resistor being varied according to a change in a resistance value of said variable resistor. 